Field of the Invention
The present invention relates to a cylinder device for controlling the change of the angular position of a swingable swash plate to vary the discharged displacement in a variable displacement compressor used for an air-cooler of an automobile or the like.
Description of the Prior Art
There is such a conventionally known variable displacement compressor in which the swinging movement of the swingable swash plate for changing the sliding stroke of an operating piston to vary the discharged displacement is controlled by a cylinder device (see U.S. Pat. No. 4,037,993).
In the above conventional cylinder device, a control piston for controlling the swinging movement of the swingable swash plate is arranged so that its inner peripheral surface is slidably guided by a driving rotary shaft and its outer peripheral surface is slidably guided by a guide member separate from the driving rotary shaft. Therefore, it is difficult to insure high accuracy of concentricity and parallelism of inner and outer guide slide surfaces of the piston. Consequently, this will cause a variation in sealing performance, a deterioration of seals, and an uneven wearing of the sliding surfaces, leading to problems of the performance and reliability of the compressor.
Another problem of the above conventional cylinder device is as follows: It is required to insure sealing properties between sliding surfaces of the cylinder and the control piston slidably fitted in the cylinder to ensure a smooth and nimble operation of the control piston, while preventing a pressurized fluid within a control pressure chamber defined by the above parts from leaking. In order to satisfy such requirements, it is necessary to increase the working accuracies of the cylinder, the control piston and peripheral parts related thereto, resulting in a substantial increase in cost.